Cooling device for vehicle rotating machine

ABSTRACT

A cooling device for a rotating machine that is to be provided in a vehicle. The cooling device includes: (a) an electric oil pump; (b) a control device configured to control operation of the electric oil pump; (c) a cooling oil passage for applying oil outputted by the electric oil pump, to a coil of the rotating machine. The control device is configured to control the operation of the electric oil pump, depending on a pressure difference between a predetermined pressure reference value and an atmospheric pressure value that is detected by an atmospheric pressure sensor.

This application claims priority from Japanese Patent Application No. 2021-127829 filed on Aug. 3, 2021, the disclosure of which is herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a cooling device for cooling a rotating machine provided in a vehicle.

BACKGROUND OF THE INVENTION

There is known a structure for cooling a coil of a rotating machine, which is to be provided in an electric vehicle or a hybrid electric vehicle, by using an oil outputted from an electric oil pump. As an example of such a structure, JP 2006-353051 A discloses a cooling device.

SUMMARY OF THE INVENTION

By the way, a higher voltage is required to be applied to the rotating machine, and a dielectric strength is required to be further increased, particularly, during running of the vehicle in highlands where an atmospheric pressure value is low. If the dielectric strength is intended to be increased by a construction, a thickness of an insulation film of the coil is required to be increased in such a construction whereby an overall size of the rotating machine could be problematically increased. Thus, it has been desired to increase the dielectric strength while suppressing increase of the overall size of the rotating machine.

The present invention was made in view of the background art described above. It is therefore an object of the present invention to provide a cooling device for a rotating machine provided in a vehicle, wherein the cooling device is capable of ensuring a dielectric strength while suppressing increase of an overall size of the rotating machine.

The above is object is achieved according to the following aspects of the present invention.

According to a first aspect of the invention, there is provided a cooling device for a rotating machine that is to be provided in a vehicle, the cooling device comprising: (a) an electric oil pump; (b) a control device configured to control operation of the electric oil pump; and (c) a cooling oil passage for applying oil outputted by the electric oil pump, to a coil of the rotating machine, wherein the control device is configured to control the operation of the electric oil pump, depending on a pressure difference between a predetermined pressure reference value and an atmospheric pressure value that is detected by an atmospheric pressure sensor.

According to a second aspect of the invention, in the cooling device according to the first aspect of the invention, the electric oil pump is to be operated with a drive current supplied to the electric oil pump, and starts to be operated when a temperature of the coil of the rotating machine becomes not lower than a start-temperature threshold value, wherein the control device is configured to change at least one of the start-temperature threshold value and a command duty ratio that is a command value of a duty ratio of the drive current supplied to the electric oil pump, depending on the pressure difference.

According to a third aspect of the invention, in the cooling device according to the first or second aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to calculate, based on the pressure difference, a first temperature difference that is an amount of change from a predetermined temperature reference value of a temperature of the coil of the rotating machine, for causing a dielectric strength of the coil to become a required dielectric-strength value, and when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to calculate, based on the pressure difference, a second temperature difference that is an amount of change from the predetermined temperature reference value of the temperature of the coil of the rotating machine, for causing the dielectric strength of the coil to become the required dielectric-strength value.

According to a fourth aspect of the invention, in the cooling device according to the third aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to reduce the start-temperature threshold value, and when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to increase the start-temperature threshold value.

According to a fifth aspect of the invention, in the cooling device according to the third aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to increase the command duty ratio, and when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to reduce the command duty ratio.

According to a sixth aspect of the invention, in the cooling device according to the fourth aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to reduce the start-temperature threshold value, by a correction amount that is increased as the first temperature difference is increased, and when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to increase the start-temperature threshold value, by a correction amount that is increased as the second temperature difference is increased.

According to a seventh aspect of the invention, in the cooling device according to the fifth aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to increase the command duty ratio, by a correction amount that is increased as the first temperature difference is increased, and when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to reduce the command duty ratio, by a correction amount that is increased as the second temperature difference is increased.

In the cooling device according to the first aspect of the invention, the operation of the electric oil pump is controlled depending on the pressure difference between the predetermined pressure reference value and the atmospheric pressure value, so that the operation of the electric oil pump is appropriately controlled. Therefore, even when the atmospheric pressure value is changed, the electric oil pump is operated depending on the change of the atmospheric pressure value whereby the temperature of the coil is adjusted depending on the atmospheric pressure value so that the dielectric strength is sufficiently ensured. Consequently, it is possible to sufficiently ensure the dielectric strength while suppressing increase of an overall size of the rotating machine.

In the cooling device according to the second aspect of the invention, at least one of the start-temperature threshold value and the command duty ratio of the electric oil pump is changed depending on the pressure difference, so that the electric oil pump can be controlled depending on the pressure difference.

In the cooling device according to the third aspect of the invention, when the atmospheric pressure value is lower than the pressure reference value, the first temperature difference that is the amount of change from the predetermined temperature reference value of the temperature of the coil of the rotating machine, for causing the dielectric strength of the coil to become the required dielectric-strength value, is calculated, based on the pressure difference, so that the required dielectric-strength value can be ensured by controlling the electric oil pump such that the temperature of the coil is reduced by the first temperature difference. Therefore, where a thickness of a film of the coil is made thin, the required dielectric-strength value can be ensured while increase of the overall size of the rotating machine is suppressed. Further, when the atmospheric pressure value is higher than the pressure reference value, the second temperature difference that is the amount of change from the predetermined temperature reference value of the temperature of the coil of the rotating machine, for causing the dielectric strength of the coil to become the required dielectric-strength value, is calculated, based on the pressure difference, so that an electric-power consumption amount can be reduced with reduction of output of the electric oil pump, by controlling the electric oil pump such that the temperature of the coil is increased by the second temperature difference.

In the cooling device according to the fourth aspect of the invention, when the atmospheric pressure value is lower than the pressure reference value, the start-temperature threshold value of the electric oil pump is corrected to be reduced whereby a start timing of the operation of the electric oil pump is advanced so that it is possible to reduce the temperature of the coil. Further, when the atmospheric pressure value is higher than the pressure reference value, the start-temperature threshold value of the electric oil pump is corrected to be increased whereby the start timing of the operation of the electric oil pump is delayed so that it is possible to reduce electric-power consumption amount by the delay of the start timing of the operation.

In the cooling device according to the fifth aspect of the invention, when the atmospheric pressure value is lower than the pressure reference value, the command duty ratio of the electric oil pump is corrected to be increased whereby a flow rate of the oil outputted from the electric oil pump is increased so that it is possible to reduce the temperature of the coil. Further, when the atmospheric pressure value is higher than the pressure reference value, the command duty ratio of the electric oil pump is corrected to be reduced whereby the flow rate of the oil outputted from the electric oil pump is reduced so that it is possible to increase the temperature of the coil.

In the cooling device according to the sixth aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the start-temperature threshold value is reduced by a correction amount that is increased as the first temperature difference is increased. As the first temperature difference is increased, the start timing of the operation of the electric oil pump is advanced more whereby the temperature of the coil can be reduced by the first temperature difference. When the atmospheric pressure value is higher than the predetermined pressure reference value, the start-temperature threshold value is increased by a correction amount that is increased as the second temperature difference is increased. As the second temperature difference is increased, the start timing of the operation of the electric oil pump is delayed more whereby the amount of the electric power consumed by the electric oil pump can be reduced in proportion with increase of the second temperature difference.

In the cooling device according to the seventh aspect of the invention, when the atmospheric pressure value is lower than the predetermined pressure reference value, the command duty ratio of the electric oil pump is increased by a correction amount that is increased as the first temperature difference is increased. As the first temperature difference is increased, the flow rate of the oil outputted from the electric oil pump is increased whereby the temperature of the coil can be reduced by the first temperature difference. When the atmospheric pressure value is higher than the predetermined pressure reference value, the command duty ratio of the electric oil pump is reduced by a correction amount that is increased as the second temperature difference is increased. As the second temperature difference is increased, the flow rate of the oil outputted from the electric oil pump is reduced whereby the amount of the electric power consumed by the electric oil pump can be reduced in proportion with increase of the second temperature difference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing construction of a driving apparatus for a vehicle to which the present invention is applied;

FIG. 2 is a view schematically showing construction of a cooling device for cooling a first rotating machine shown in FIG. 1 , and also a control system of an electronic control device for controlling an electric oil pump of the cooling device;

FIG. 3 is a view showing a relationship between an atmospheric pressure value and a dielectric strength of a coil of the rotating machine;

FIG. 4 is a view showing a relationship between a temperature of the coil and the dielectric strength of the coil; and

FIG. 5 is a flow chart showing a main part of a control routine executed by the electronic control device, namely, a control routine that is executed for ensuring the dielectric strength even during running of the vehicle in highlands without increasing an overall size of the rotating machine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Hereinafter, a preferred embodiment of the invention will be described in detail with reference to the accompanying drawings. The figures of the drawings are simplified or deformed as needed, and each portion is not necessarily precisely depicted in terms of dimension ratio, shape, etc.

Embodiment

FIG. 1 is a view schematically showing construction of a vehicle driving apparatus 10 to which the present invention is applied. The driving apparatus 10 is configured to transmit powers of drive power sources in the form of an engine 12 and a second rotating machine MG2, to right and left front wheels 14 r, 14 l (hereinafter referred simply to as “front wheels 14” unless they are to be distinguished from each other). The driving apparatus 10 is to be advantageously used for a hybrid electric vehicle with FF (front engine/front drive) system. It is noted that the term “power” corresponds to “force” or “drive power” in description of the present specification.

As shown in FIG. 1 , the driving apparatus 10 includes an input shaft 23, a planetary gear device 24, a first rotating machine MG1 and an output gear 26, which are disposed to be rotatable about a first axis CL1. The driving apparatus 10 further includes a power transmission shaft 34, the above-described second rotating machine MG2 and a reduction gear 36, which are disposed to be rotatable about a second axis CL2, wherein the reduction gear 36 is mounted on the power transmission shaft 34. The driving apparatus 10 further includes a counter shaft 32, a counter gear 28 and a differential drive gear 30, which are disposed to be rotatable about a third axis CL3, wherein the counter gear 28 and the differential drive gear 30 are mounted on the counter shaft 32. The driving apparatus 10 further includes a differential device 20 and axles 22 r, 22 l, which are disposed to be rotatable about a fourth axis CL4. All of these rotary members are disposed inside the casing 40 as a non-rotary member. Any one of the first through fourth axes CL1-CL4 is a rotary axis that is parallel to a direction of width of the vehicle.

Each of the first and second rotating machines MG1, MG2 may be a rotating machine having a function of a motor operable to convert an electric energy into a mechanical drive power and/or a function of a generator operable to convert a mechanical drive power into an electric energy, and preferably, is a motor generator having both of the functions so as to be operated as a selected one of the motor and the generator. In the present embodiment, the first rotating machine MG1 has a function of an electric generator operable to receive a reaction force from the engine 12, and a function of a rotating machine operable to start the engine 12 while the engine 12 is at rest. Meanwhile, the second rotating machine MG2 has a function of a rotating machine functioning as a drive power source to generate a drive power, and a function of an electric generator operable to perform a regenerative operation for converting a reverse drive power received from the front wheels 14, into an electric energy. It is noted that each of the first and second rotating machines MG1, MG2 corresponds to “rotating machine” recited in the appended claims.

The input shaft 23 is connected to the engine 12 through a crank shaft 12 a of the engine 12 and a damper (not shown), for example, in a power transmittable manner. The input shaft 23 is held by the casing 40 through a bearing 18, for example, and is rotatable about the first axis CL1.

The planetary gear device 24, which is disposed to be coaxial with the first axis CL1, is a single-pinion type planetary gear device (differential mechanism) that includes a sun gear S, a carrier CA and a ring gear R. The planetary gear device 24 serves as a power distributing mechanism configured to distribute the power of the engine 12 to the first rotating machine MG1 and the output gear 26. The sun gear S of the planetary gear device 24 is connected to the first rotating machine MG1 in a power transmittable manner. The carrier CA of the planetary gear device 24 is connected to the engine 12 through, for example, the input shaft 23 and the crank shaft 12 a in a power transmittable manner. The ring gear R of the planetary gear device 24 is connected to the output gear 26 in a power transmittable manner. It is noted that the ring gear R and the output gear 26 are formed integrally with each other, namely, are constituted by a compound gear.

The first rotating machine MG1 is disposed in a position adjacent to the planetary gear device 24, with a partition wall 56 (that is a part of the casing 40) being located between the first rotating machine MG1 and the planetary gear device 24 in a direction of the first axis CL1. The first rotating machine MG1 includes an annular-shaped stator 42 that is unrotatably fixed to the casing 40, an annular-shaped rotor 44 disposed on an inner peripheral side of the stator 42, and a rotor shaft 46 connected to an inner periphery of the rotor 44. The stator 42 is provided with a stator coil 48 wound thereon. The rotor shaft 46 is held at its axially opposite end portions by the casing 40 through a pair of bearings 47 a, 47 b, such that the rotor shaft 46 is rotatable about the first axis CL1. It is noted that the stator coil 48 correspond to “coil (of the rotating machine)” recited in the appended claims.

The output gear 26 is connected to the ring gear R of the planetary gear device 24, and meshes with the counter gear 28 that is disposed on the counter shaft 32.

The second rotating machine MG2 and the reduction gear 36 are disposed to be rotatable about the second axis CL2, and are adjacent to each other with the partition wall 56 being located therebetween in a direction of the second axis CL2. The second rotating machine MG2 and the reduction gear 36 are connected to each other through the power transmission shaft 34 in a power transmittable manner.

The second rotating machine MG2 includes an annular-shaped stator 50 that is unrotatably fixed to the casing 40, an annular-shaped rotor 52 disposed on an inner peripheral side of the stator 50, and a rotor shaft 54 connected to an inner periphery of the rotor 52. The stator 50 is provided with a stator coil 55 wound thereon. The rotor shaft 54 is held at its axially opposite end portions by the casing 40 through a pair of bearings 57 a, 57 b, such that the rotor shaft 54 is rotatable about the second axis CL2. It is noted that the stator coil 55 correspond to the “coil(of the rotating machine)” recited in the appended claims.

The reduction gear 36 is formed integrally with the power transmission shaft 34, and meshes with the counter gear 28 disposed on the counter shaft 32. The number of teeth of the reduction gear 36 is smaller than the number of teeth of the counter gear 28. Thus, rotation of the second rotating machine MG2 is transmitted to the counter shaft 32 through the reduction gear 36 and the counter gear 28, such that a rotational speed of the counter shaft 32 is made lower than a rotational speed of the second rotating machine MG2. The power transmission shaft 34 is held at its axially opposite end portions by the casing 40 through a pair of bearings 59 a, 59 b, such that the power transmission shaft 34 is rotatable about the second axis CL2.

The counter shaft 32 is held at its axially opposite end portions by the casing 40 through a pair of bearings 61 a, 61 b, such that the counter shaft 32 is rotatable about the third axis CL3.

The counter gear 28 and the differential drive gear 30 are disposed on the counter shaft 32, unrotatably relative to the counter shaft 32 that is to be rotated about the third axis CL3. The counter gear 28 meshes with the output gear 26 and the reduction gear 36 so that the power outputted from the engine 12 and/or the power outputted from the second rotating machine MG2 are to be transmitted. The differential drive gear 30 meshes with a differential driven gear 38 of the differential device 20. Thus, when the power transmitted to the counter gear 28 from the output gear 26 and/or the reduction gear 36, the power is transmitted to the differential device 20 through the counter shaft 32 and the differential drive gear 30.

The differential device 20 and the right and left axles 22 r, 22 l are disposed to be rotatable about the fourth axis CL4. With the differential driven gear 38 of the differential device 20 meshing with the differential drive gear 30, the power of the engine 12 and/or the power of the second rotating machine MG2 is transmitted to the differential device 20 through the differential driven gear 38.

The differential device 20 is constituted by a well-known differential mechanism, and is configured to transmit the power to the right and left axles 22 r, 22 l while allowing rotation of each one of the axles 22 r, 22 l relative to the other of the axles 22 r, 22 l. The differential device 20 is held, at its opposite end portions that are opposite to each other in the direction of the fourth axis CL4, by the casing 40 through a pair of bearings 62 a, 62 b, such that the differential device 20 is rotatable about the fourth axis CL4. It is noted that detailed description of the differential device 20, which is a known device, is not provided.

The casing 40 of the driving apparatus 10 is constituted by a first casing member 40 a, a second casing member 40 b and a third casing member 40 c that are fixed to one another. The second casing member 40 b opens in its opposite ends that are opposite to each other in the direction of the first axis CL1. The second casing member 40 b is fixedly connected at one of the openings to the first casing member 40 a through screw bolts, such that the one of the openings is enclosed by the first casing member 40 a. The second casing member 40 b is fixedly connected at the other of the openings to the third casing member 40 c through screw bolts, such that the other of the openings is enclosed by the third casing member 40 c.

The second casing member 40 b is provided with the partition wall 56 that is substantially perpendicular to the first axis CL1. By provision of the partition wall 56, an interior of the casing 40 is sectioned into a gear room 58 and a motor room 60, such that the gear room 58 is covered by the first casing member 40 a and the second casing member 40 b while the motor room 60 is covered by the second casing member 40 b and the third casing member 40 c. Various gears or devices such as the planetary gear device 24, output gear 26, counter gear 28, reduction gear 36 and differential device 20 are disposed in the gear room 58. The first and second rotating machines MG1, MG2 are disposed in the motor room 60.

The driving apparatus 10 further includes a mechanical oil pump MOP which is to be driven by the engine 12. The oil pump MOP is disposed on the first axis CL1, and is located on a side of one of axially opposite end portions of the input shaft 23, which is remote from the engine 12. The oil pump MOP includes a drive gear (not shown) that is connected to the above-described one of the axially opposite end portions of the input shaft 23, so that the oil pump MOP is to be driven by rotation of the engine 12. The driving apparatus 10 further includes an electric oil pump EOP including an electric motor 64. The electric oil pump EOP, i.e., the electric motor 64 is to be operated or driven by a drive current controlled by an electronic control device 90 that is described below. The electric oil pump EOP is to be driven, for example, in a BEV running mode in which the engine 12 is not driven.

In the driving apparatus 10 constructed as described above, the power of the engine 12 is transmitted to the right and left front wheels 14 r. 14 l through the planetary gear device 24, output gear 26, counter gear 28, counter shaft 32, differential drive gear 30, differential device 20 and axles 22 r, 22 l in this order of description. Further, the power of the second rotating machine MG2 is transmitted to the right and left front wheels 14 r. 14 l through the rotor shaft 54, power transmission shaft 34, reduction gear 36, counter gear 28, counter shaft 32, differential drive gear 30, differential device 20 and front axles 22 r, 22 l in this order of description.

FIG. 2 is a view schematically showing construction of the cooling device 70 for cooling the first and second rotating machines MG1, MG2, and also a control system of the electronic control device 90 for controlling the electric oil pump EOP. In FIG. 2 , an upward direction in the drawing sheet corresponds to a vertically upward direction in a state in which the cooling device 70 is disposed in a predetermined position in the vehicle that is on a flat road. Since structures for cooling the respective first and second rotating machines MG1, MG2 by using oil are identical with each other, only one of them for cooling the first rotating machine MG1 is shown in FIG. 2 while the other for cooling the second rotating machine MG2 is not shown in FIG. 2 .

FIG. 2 shows a cross section of a part of the first rotating machine MG1 disposed in the motor room 60 that is provided inside the casing 40. The first rotating machine MG1 is disposed to be rotatable about the first axis CL1, and includes a cylindrical-shaped stator 42 fixed to the casing 40, and a rotor 44 disposed on an inner peripheral side of the stator 42. Each of the stator 42 and the rotor 44 is constituted by a plurality of disc-shaped electromagnetic steel sheets that are laminated on each other in the direction of the first axis CL1.

The stator 42 has a plurality of slots (grooves) that are provided in its inner peripheral portion and are parallel to the first axis CL1, and conductor wires constituting the stator coil 48 pass through the plurality of slots. A pair of coil ends 72, each of which is formed by bundling the conductor wires, are provided on respective opposite sides of the stator 42 in the direction of the first axis CL1. The stator 42 is provided with the stator coil 48 wound thereon.

When the first rotating machine MG1 is driven, the stator coil 48 is energized so as to be heated. A heat generated in the stator coil 48 is dissipated by being transferred to the stator 42, for example. Meanwhile, a heat generated in each of the coil ends 72 is unlikely to be dissipated, because the coil ends 72 are not in contact with the stator 42. However, in the cooling device 70 according to the present embodiment, a cooling pipe 74 is provided on an upper side of the first rotating machine MG1 in the vertical direction (in the state in the vehicle is on a flat road), and the oil is released from the cooling pipe 74 toward the coil ends 72 of the first rotating machine MG1. Thus, with the oil being applied directly to the coil ends 72, the stator coil 48 of the first rotating machine MG1 is directly cooled.

The cooling device 70 includes the cooling pipe 74 that is disposed above the first rotating machine MG1 in the vertical direction. The cooling pipe 74 is constituted by a hollow member having an opening in one of its axially opposite ends, and is disposed in parallel to the first axis CL1. The cooling pipe 74 is fixed at the one of the axially opposite ends to the partition wall 56 of the second casing member 40 b through screw bolts 76. The cooling pipe 74 has a protrusion 78 in the other of the axially opposite ends. With the protrusion 78 being fitted in a recess 80 provided in the third casing member 40 c, swing or sway of the cooling pipe 74 is suppressed.

The oil, which is outputted from the electric oil pump EOP, is supplied to the cooling pipe 74 via the above-described opening provided in the one of the axially opposite ends. It is noted that the oil outputted from the electric oil pump EOP may be adapted to pass through an oil cooler (not shown) so as to be cooled, before being supplied to the cooling pipe 74.

The cooling pipe 74 has a plurality of cooling oil holes 82 so that the oil flowing into the cooling pipe 74 is to be applied directly to the pair of coil ends 72 through the cooling oil holes 82. Each of the cooling oil holes 82 communicates inside and outside of the cooling pipe 74, and opens in a position that is opposed to a corresponding one of the coil ends 72 of the first rotating machine MG1. Specifically described, each of the cooling oil holes 82 is located in substantially the same position as a corresponding one of the coil ends 72 in a longitudinal direction of the cooling pipe 74, i.e., in the direction of the first axis CL1. That is, each of the cooling oil holes 82 is located in a position overlapping with a corresponding one of the coil ends 72 as seen in a radial direction of the first axis CL1. With each of the cooling oil holes 82 being located in the above-described position, the oil flowing into the cooling pipe 74 is released through each of the cooling oil holes 82 toward a corresponding one of the coil ends 72, as indicated by arrows shown in FIG. 2 . Thus, the oil released through the cooling oil holes 82 is applied directly to the coil ends 72. It is noted that the cooling pipe 74 and the cooling oil holes 82 provided in the cooling pipe 74 cooperate to constitute a cooling oil passage 84for applying the oil outputted by the electric oil pump EOP, to the stator coil 48 of the first rotating machine MG1.

A flow rate of the oil supplied into the cooling pipe 74 is controlled by the electric oil pump EOP. More specifically, the flow rate of the oil supplied into the cooling pipe 74 is controlled through a duty ratio of the drive current applied to the electric oil pump EOP. For example, with the flow rate of the oil outputted from the electric oil pump EOP being increased, the flow rate of the oil supplied into the cooling pipe 74 is increased whereby the flow rate of the oil released from the cooling oil holes 82 toward the coil ends 72 is increased. With the flow rate of the oil applied to the coil ends 72 being increased, a rate of dissipation of heat from the coil ends 72 through the applied oil is increased whereby a rate of cooling of the coil ends 72 is increased.

The operation of the electric oil pump EOP is controlled by the electronic control device 90. The electronic control device 90 includes a so-called microcomputer incorporating a CPU, a ROM, a RAM and an input-output interface. The CPU controls the operation of the electric oil pump EOP, by processing various input signals, according to a control program stored in the ROM, while utilizing a temporary data storage function of the RAM. It is noted that the electronic control device 90 may be either a control device provided for controlling exclusively the electric oil pump EOP, or a control device provided for not only controlling the electric oil pump EOP but also performing other control operations in the vehicle. The cooling device 70 includes the electric oil pump EOP, the electronic control device 90 configured to control the operation of the electric oil pump EOP, and the cooling oil passage 84. It is noted that the electronic control device 90 corresponds to “control device” recited in the appended claims.

The electronic control device 90 receives various signals such as a signal indicative of a coil temperature Tcoil of the stator coil 48 and supplied from a rotating-machine temperature sensor 92 that is configured to detect the coil temperature Tcoil, and a signal indicative of an atmospheric pressure value Pair and supplied from an atmospheric pressure sensor 94 that is configured to detect the atmospheric pressure value Pair. Meanwhile, the electronic control device 90 outputs a command signal Seop that is to be supplied to the electric motor 64, for driving the electric oil pump EOP. The command signal Seop includes a command duty ratio Rduty that is a command value of the duty ratio of the drive current supplied to the electric oil pump EOP. With the command duty ratio Rduty being controlled, a rotational speed of the electric oil pump EOP is controlled. For example, with the command duty ratio Rduty being increased, the rotational speed of the electric oil pump EOP is increased whereby the flow rate of the oil outputted from the electric oil pump EOP is increased.

By the way, a higher voltage is required to be applied to the rotating machine MG, and accordingly a dielectric strength Vins of the stator coil 48 is required to be increased for enabling the higher voltage to be applied to the rotating machine MG. It is noted that the dielectric strength Vins (that is also known as dielectric voltage or withstand voltage) is a value representing a capacity of an insulation material (that is a film covering the stator coil 48 in the present embodiment) for withstanding the voltage. In the present embodiment, the dielectric strength Vins is treated as a voltage value (withstand voltage) that the stator coil 48 can withstand. As a means for increasing the dielectric strength Vins [V], for example, it might be possible to increase a thickness of the film of the stator coil 48. It is known that the dielectric strength Vins is reduced during running of the vehicle in highlands where the atmospheric pressure value Pair is low. Therefore, if the thickness of the film of the stator coil 48 is determined such that the dielectric strength Vins is sufficiently ensured even in the highlands, the determined thickness would have to be further increased so that an overall size of the rotating machine MG would be inevitably increased.

In the present embodiment, the electronic control device 90 functionally includes a pump control means in the form of a pump control portion 100 that is configured to control the operation of the electric oil pump EOP, depending on a pressure difference ΔP (=P−P0) that is a difference of the atmospheric pressure value Pair detected by the atmospheric pressure sensor 94, relative to a predetermined pressure reference value P0. There will be described an operation that is to be executed by the pump control portion 100, for controlling the electric oil pump EOP.

FIG. 3 shows a relationship between the atmospheric pressure value Pair and the dielectric strength Vins, wherein its horizontal axis represents the atmospheric pressure value Pair while its vertical axis represents the dielectric strength Vins [V]. In FIG. 3 , solid line represents the relationship in a case in which the thickness of the film of the stator coil 48 is determined in accordance with a conventional design, while broken line represents the relationship in a case in which the thickness of the film of the stator coil 48 corresponds to a thickness value in the present embodiment. The thickness of the film in the conventional design is large because the thickness is determined in view of a minimum pressure value Plow that is estimated in the highlands. Meanwhile, the thickness of the film in the present embodiment is smaller than that in accordance with the conventional design. As shown in FIG. 3 , both in the solid line representing the relationship in the conventional design and the broken line representing the relationship in the present embodiment, the dielectric strength Vins is increased as the atmospheric pressure value Pair is increased.

There will be first described the case of the conventional design in which the above-describe relationship is represented by the solid line in FIG. 3 . The thickness of the film of the stator coil 48 in the conventional design is larger than the thickness of the film of the stator coil 48 in the present embodiment in which the above-described relationship is represented by broken line in FIG. 3 , so that the dielectric strength Vins in the conventional design is higher than the dielectric strength Vins in the present embodiment, where they are compared with each other at a same value of the atmospheric pressure value Pair. In the conventional design, the thickness of the film of the stator coil 48 is determined such that the dielectric strength Vins is substantially equal to a predetermined required dielectric-strength value Vlim when the atmospheric pressure value Pair is the minimum pressure value Plow that is a minimum pressure value estimated during running of the vehicle, so that the dielectric strength Vins is not smaller than the required dielectric-strength value Vlim in all atmospheric pressure ranges during running of the vehicle. However, as the trade-off, the thickness of the film of the stator coil 48 is so large that the overall size of the rotating machine MG becomes so large. It is noted that the required dielectric-strength value Vlim is a predetermined value which is obtained by experimentation or determined by an appropriate design theory and which is large enough to withstand a surge pressure caused transiently in the stator coil 48, for example.

On the other hand, in the present embodiment, the operation of the electric oil pump EOP is controlled depending on the pressure difference ΔP between the atmospheric pressure value Pair and the pressure reference value P0, as described above. This control arrangement makes it possible to make the thickness of the film of the stator coil 48 smaller than that in the conventional design.

In FIG. 3 , the broken line represents the relationship between the atmospheric pressure value Pair and the dielectric strength Vins of the stator coil 48 in the present embodiment. In the present embodiment, with reduction of the thickness of the film of the stator coil 48, the dielectric strength Vins is smaller than that in the conventional design, and the dielectric strength Vins is smaller than the required dielectric-strength value Vlim in a range in which the atmospheric pressure value Pair is lower than the pressure reference value P0. For example, when the atmospheric pressure value Pair is an atmospheric pressure value P1 that is lower than the pressure reference value P0, the pressure difference ΔP1 (=P1−P0) is a negative value, so that the dielectric strength Vins is smaller than the required dielectric-strength value Vlim by an electric voltage difference ΔV1. Thus, in the range in which the atmospheric pressure value Pair is lower than the pressure reference value P0, the dielectric strength Vins is smaller than the required dielectric-strength value Vlim. On the other hand, in a range in which the atmospheric pressure value Pair is higher than the pressure reference value P0, the dielectric strength Vins is larger than the required dielectric-strength value Vlim. For example, when the atmospheric pressure value Pair is an atmospheric pressure value P2 that is higher than the pressure reference value P0, the pressure difference ΔP2 (=P2−P0) is a positive value, so that the dielectric strength Vins is larger than the required dielectric-strength value Vlim by an electric voltage difference ΔV2.

The pressure reference value P0 is a predetermined value which is obtained by experimentation or determined by an appropriate design theory such that the dielectric strength Vins of the stator coil 48 of the present embodiment corresponds to the required dielectric-strength value Vlim when the atmospheric pressure value Pair is the pressure reference value P0. Further, based on the relationship represented by the broken line in FIG. 3 , a change rate α of the dielectric strength Vins relative to the atmospheric pressure value Pair is obtained. With the change rate α being obtained, it is possible to obtain the electric voltage difference ΔV (electric voltage difference ΔV1, electric voltage difference ΔV2) that corresponds to a difference relative to the required dielectric-strength value Vlim, by multiplying the pressure difference ΔP (=Pair−P0) by the obtained change rate α.

FIG. 4 shows a relationship between the coil temperature Tcoil and the dielectric strength Vins of the stator coil 48. In FIG. 4 , its horizontal axis represents the coil temperature Tcoil of the stator coil 48 while its vertical axis represents the dielectric strength Vins of the stator coil 48. As shown in FIG. 4 , the dielectric strength Vins is reduced as the coil temperature Tcoil is increased. In FIG. 4 , the temperature reference value T0 of the coil temperature Tcoil is a predetermined value corresponding to the highest value of a range that makes it possible to obtain the required dielectric-strength value Vlim irrespective of the atmospheric pressure value Pair during running of the vehicle. That is, the temperature reference value T0 corresponds to the highest value of the range that makes the dielectric strength Vins of the stator coil 48 not smaller than the required dielectric-strength value Vlim in an atmospheric pressure range that is estimated during running of the vehicle. At a coil temperature T1 that is lower than the temperature reference value T0 by a temperature difference ΔT1, the dielectric strength Vins is made larger than the required dielectric-strength value Vlim by the electric voltage difference ΔV1. In other words, with the coil temperature Tcoil being reduced by the temperature difference ΔT1, the dielectric strength Vins is made larger than the required dielectric-strength value Vlim by the electric voltage difference ΔV1. On the other hand, at a coil temperature T2 that is higher than the temperature reference value T0 by a temperature difference ΔT2, the dielectric strength Vins is made smaller than the required dielectric-strength value Vlim by the electric voltage difference ΔV2. In other words, with the coil temperature Tcoil being increased by the temperature difference ΔT2, the dielectric strength Vins is made smaller than the required dielectric-strength value Vlim by the electric voltage difference ΔV2.

Further, based on the relationship shown in FIG. 4 , a change rate β of the dielectric strength Vins relative to the coil temperature Tcoil is obtained. With the change rate β being obtained, it is possible to obtain a required value of the temperature difference ΔT that is required to change the dielectric strength Vins to a sum of the required dielectric-strength value Vlim and the electric voltage difference ΔV, by dividing the electric voltage difference ΔV by the obtained change rate β (ΔV/β).

Based on FIG. 3 and FIG. 4 , it is possible to obtain the required value of the temperature difference ΔT that is required to ensure the required dielectric-strength value Vlim, depending on the pressure difference ΔP between the atmospheric pressure value Pair and the pressure reference value P0, namely, it is possible to obtain the required value of the temperature difference ΔT by which the coil temperature of the stator coil 48 is to be changed, depending on the pressure difference ΔP between the atmospheric pressure value Pair and the pressure reference value P0. In the following description, the atmospheric pressure value Pair lower than the pressure reference value P0 will be referred to as the atmospheric pressure value P1, the pressure difference ΔP between the atmospheric pressure value P1 and the pressure reference value P0 will be referred to as the first pressure difference ΔP1, the electric voltage difference ΔV calculated based on the first pressure difference ΔP1 will be referred to as the first electric voltage difference ΔV1, and the temperature difference ΔT calculated based on the first electric voltage difference ΔV1 will be referred to as the first temperature difference ΔT1. Further, the atmospheric pressure value Pair higher than the pressure reference value P0 will be referred to as the atmospheric pressure value P2, the pressure difference ΔP between the atmospheric pressure value P2 and the pressure reference value P0 will be referred to as the second pressure difference ΔP2, the electric voltage difference ΔV calculated based on the second pressure difference ΔP2 will be referred to as the second electric voltage difference ΔV2, and the temperature difference ΔT calculated based on the second electric voltage difference ΔV2 will be referred to as the second temperature difference ΔT2.

There will be first described a process of calculation of the first temperature difference ΔT1 in a case in which the atmospheric pressure value Pair is the atmospheric pressure value P1 lower than the pressure reference value P0. The process is initiated by calculating the first pressure difference ΔP1(=P1−P0). Then, the first electric voltage difference ΔV1 is calculated by multiplying the first pressure difference ΔP1 by the change rate α that is obtained from the relationship shown in FIG. 3 (ΔV1=α×ΔP1). Since the atmospheric pressure value Pair is the atmospheric pressure value P1 lower than the pressure reference value P0 in this case, the first electric voltage difference ΔV1 corresponds to an insufficient electric voltage difference for the required dielectric-strength value Vlim. Then, the first temperature difference ΔT1, by which the coil temperature of the stator coil 48 is required to be reduced for compensating the first electric voltage difference ΔV1, is calculated, by dividing the first electric voltage difference ΔV1 by the change rate β that is obtained from the relationship shown in FIG. 4 (ΔT1=ΔV1/β).

Thus, in the case in which the atmospheric pressure value Pair is lower than the pressure reference value P0, the first temperature difference ΔT1, which is an amount of reduction (change) from the temperature reference value T0 of the coil temperature Tcoil, for causing the dielectric strength Vins of the stator coil 48 to become the required dielectric-strength value Vlim, is calculated based on the first pressure difference ΔP1.

There will be next described a process of calculation of the second temperature difference ΔT2 in a case in which the atmospheric pressure value Pair is the atmospheric pressure value P2 higher than the pressure reference value P0. The process is initiated by calculating the second pressure difference ΔP2 (=P2−P0). Then, the second electric voltage difference ΔV2 is calculated by multiplying the second pressure difference ΔP2 by the change rate α that is obtained from the relationship shown in FIG. 3 (ΔV2=α×ΔP2). Since the atmospheric pressure value Pair is the atmospheric pressure value P2 higher than the pressure reference value P0 in this case, the second electric voltage difference ΔV2 corresponds to a surplus electric voltage difference for the required dielectric-strength value Vlim. Then, the second temperature difference ΔT2, by which the coil temperature of the stator coil 48 is allowed to be increased, is calculated, by dividing the second electric voltage difference ΔV2 by the change rate β that is obtained from the relationship shown in FIG. 4 (ΔT2=ΔV2/β).

Thus, in the case in which the atmospheric pressure value Pair is higher than the pressure reference value P0, the second temperature difference ΔT2, which is an amount of increase (change) from the temperature reference value T0 of the coil temperature Tcoil, for causing the dielectric strength Vins of the stator coil 48 to become the required dielectric-strength value Vlim, is calculated based on the second pressure difference ΔP2.

As described above, when the atmospheric pressure value Pair is higher than the pressure reference value P0, the dielectric strength Vins becomes larger than the required dielectric-strength value Vlim by the second electric voltage difference ΔV2. In this case, with the coil temperature Tcoil of the stator coil 48 being increased by the second temperature difference ΔT2, the dielectric strength Vins becomes the required dielectric-strength value Vlim.

The pump control portion 100 determines whether the atmospheric pressure value Pair detected by the atmospheric pressure sensor 94 is lower than the pressure reference value P0 or not. That is, the pump control portion 100 determines whether the pressure difference ΔP (=Pair−P0) of the atmospheric pressure value Pair relative to the pressure reference value P0 is a negative value or not. When the pressure difference ΔP is a negative value, the pump control portion 100 multiplies the pressure difference ΔP by the change rate α that is obtained from the relationship shown in FIG. 3 , so as to calculate the first electric voltage difference ΔV1 as the insufficient electric voltage difference for the required dielectric-strength value Vlim. Then, the pump control portion 100 calculates the first temperature difference ΔT1 (by which the coil temperature Tcoil of the stator coil 48 is required to be reduced for ensuring the required dielectric-strength value Vlim), by dividing the first electric voltage difference ΔV1 by the change rate β that is obtained from the relationship shown in FIG. 4 .

After having calculated the first temperature difference ΔT1, the pump control portion 100 calculates a correction amount ΔTeops1 of a start-temperature threshold value Teops of the electric oil pump EOP, by applying the first temperature difference ΔT1 into a pre-stored relational map representing a relationship between the first temperature difference ΔT1 and the correction amount ΔTeops1 of the start-temperature threshold value Teops of the electric oil pump EOP. The pump control portion 100 corrects the start-temperature threshold value Teops as a currently set value, to a corrected value (=Teops−ΔTeops1) that is obtained by subtracting the correction amount ΔTeops1 from the start-temperature threshold value Teops as the currently set value. Then, the pump control portion 100 starts the operation of the electric oil pump EOP when the coil temperature Tcoil of the stator coil 48 becomes the corrected value (=Teops−ΔTeops1). Consequently, since a start timing of the operation of the electric oil pump EOP is advanced, the stator coil 48 is cooled early whereby the coil temperature Tcoil of the stator coil 48 can be reduced by the first temperature difference ΔT1. It is noted that the relational map representing the relationship between the first temperature difference ΔT1 and the correction amount ΔTeops1 of the start-temperature threshold value Teops is a predetermined map that is obtained by experimentation or determined by an appropriate design theory such that the correction amount ΔTeops1 of the start-temperature threshold value Teops makes it possible to reduce the coil temperature Tcoil of the stator coil 48 by the first temperature difference ΔT1. In the relational map, the correction amount ΔTeops1 is increased in proportion with increase of the first temperature difference ΔT1.Thus, when the atmospheric pressure value Pair is lower than the pressure reference value P0, the correction amount ΔTeops1, by which the start-temperature threshold value Teops is to be reduced, is increased with increase of the first temperature difference ΔT1 (absolute value), whereby the corrected value of the start-temperature threshold value Teops is reduced more as the first temperature difference ΔT1 is increased.

Alternatively, after having calculated the first temperature difference ΔT1, the pump control portion 100 calculates a correction amount ΔRduty1 of the command duty ratio Rduty (that is the command value of the duty ratio of the drive current supplied to the electric oil pump EOP), by applying the first temperature difference ΔT1 into a pre-stored relational map representing a relationship between the first temperature difference ΔT1 and the correction amount ΔRduty1 of the command duty ratio Rduty. The pump control portion 100 corrects the command duty ratio Rduty as a currently set value, to a corrected value (=Rduty+ΔRduty1) that is obtained by adding the correction amount ΔRduty1 to the command duty ratio Rduty as the currently set value. Then, when the electric oil pump EOP is to be operated, the pump control portion 100 causes the electric oil pump EOP to be operated with the corrected value of the command duty ratio Rduty. Consequently, since the rotational speed of the electric oil pump EOP is increased, the flow rate of the oil outputted from the electric oil pump EOP is increased whereby the coil temperature Tcoil of the stator coil 48 can be reduced by the first temperature difference ΔT1. It is noted that the relational map representing the relationship between the first temperature difference ΔT1 and the correction amount ΔRduty1 of the command duty ratio Rduty is a predetermined map that is obtained by experimentation or determined by an appropriate design theory such that the correction amount ΔRduty1 of the command duty ratio Rduty makes it possible to reduce the coil temperature Tcoil of the stator coil 48 by the first temperature difference ΔT1. In the relational map, the correction amount ΔRduty1 is increased in proportion with increase of the first temperature difference ΔT1. Thus, when the atmospheric pressure value Pair is lower than the pressure reference value P0, the correction amount ΔRduty1, by which the command duty ratio Rduty is to be increased, is increased with increase of the first temperature difference ΔT1 (absolute value), whereby the corrected value of the command duty ratio Rduty is increased more as the first temperature difference ΔT1 is increased.

Further, when the pressure difference ΔP (=Pair−P0) is a positive value, the pump control portion 100 multiplies the pressure difference ΔP by the change rate α that is obtained from the relationship shown in FIG. 3 , so as to calculate the second electric voltage difference ΔV2 as the surplus electric voltage difference for the required dielectric-strength value Vlim. Then, the pump control portion 100 calculates the second temperature difference ΔT2 (by which the coil temperature Tcoil of the stator coil 48 is allowed to be increased), by dividing the second electric voltage difference ΔV2 by the change rate β that is obtained from the relationship shown in FIG. 4 .

After having calculated the second temperature difference ΔT2, the pump control portion 100 calculates a correction amount ΔTeops2 of the start-temperature threshold value Teops of the electric oil pump EOP, by applying the second temperature difference ΔT2 into a pre-stored relational map representing a relationship between the second temperature difference ΔT2 and the correction amount ΔTeops1 of the start-temperature threshold value Teops of the electric oil pump EOP. The pump control portion 100 corrects the start-temperature threshold value Teops as a currently set value, to a corrected value (=Teops+ΔTeops2) that is obtained by adding the correction amount ΔTeops2 to the start-temperature threshold value Teops as the currently set value. Then, the pump control portion 100 starts the operation of the electric oil pump EOP when the coil temperature Tcoil of the stator coil 48 becomes the corrected value (=Teops+ΔTeops2). Consequently, since the start timing of the operation of the electric oil pump EOP is delayed, an electric-power consumption amount is reduced by an amount corresponding to reduction of an operation time of the electric oil pump EOP. Further, although the coil temperature Tcoil of the stator coil 48 is increased by the delay of the start timing of the operation of the electric oil pump EOP, the increase of the coil temperature Tcoil is suppressed to the second temperature difference ΔT2 whereby the dielectric strength Vins is prevented from being smaller than the required dielectric-strength value Vlim, namely, the required dielectric-strength value Vlim is ensured. It is noted that the relational map representing the relationship between the second temperature difference ΔT2 and the correction amount ΔTeops2 of the start-temperature threshold value Teops is a predetermined map that is obtained by experimentation or determined by an appropriate design theory such that the correction amount ΔTeops2 of the start-temperature threshold value Teops makes it possible to increase the coil temperature Tcoil of the stator coil 48 by the second temperature difference ΔT2.In the relational map, the correction amount ΔTeops2 is increased in proportion with increase of the second temperature difference ΔT2. Thus, when the atmospheric pressure value Pair is higher than the pressure reference value P0, the correction amount ΔTeops2, by which the start-temperature threshold value Teops is to be increased, is increased with increase of the second temperature difference ΔT2 (absolute value), whereby the corrected value of the start-temperature threshold value Teops is increased more as the second temperature difference ΔT2 is increased.

Alternatively, after having calculated the second temperature difference ΔT2, the pump control portion 100 calculates a correction amount ΔRduty2 of the command duty ratio Rduty (that is the command value of the duty ratio of the drive current supplied to the electric oil pump EOP), by applying the second temperature difference ΔT2 into a pre-stored relational map representing a relationship between the second temperature difference ΔT1 and the correction amount ΔRduty2 of the command duty ratio Rduty. The pump control portion 100 corrects the command duty ratio Rduty as a currently set value, to a corrected value (=Rduty−ΔRduty2) that is obtained by subtracting the correction amount ΔRduty2 from the command duty ratio Rduty as the currently set value. Then, when the electric oil pump EOP is to be operated, the pump control portion 100 causes the electric oil pump EOP to be operated with the corrected value of the command duty ratio Rduty. Consequently, since the rotational speed of the electric oil pump EOP is reduced, the flow rate of the oil outputted from the electric oil pump EOP is reduced whereby the coil temperature Tcoil of the stator coil 48 can be increased by the second temperature difference ΔT2. In this instance, the increase of the coil temperature Tcoil does not exceed the second temperature difference ΔT2, the dielectric strength Vins is prevented from being smaller than the required dielectric-strength value Vlim. It is noted that the relational map representing the relationship between the second temperature difference ΔT2 and the correction amount ΔRduty2 of the command duty ratio Rduty is a predetermined map that is obtained by experimentation or determined by an appropriate design theory such that the correction amount ΔRduty2 of the command duty ratio Rduty makes it possible to increase the coil temperature Tcoil of the stator coil 48 by the second temperature difference ΔT2.In the relational map, the correction amount ΔRduty2 is increased in proportion with increase of the second temperature difference ΔT2. Thus, when the atmospheric pressure value Pair is higher than the pressure reference value P0, the correction amount ΔRduty2, by which the command duty ratio Rduty is to be reduced, is increased with increase of the second temperature difference ΔT2 (absolute value), whereby the corrected value of the command duty ratio Rduty is reduced more as the second temperature difference ΔT2 is increased.

Thus, as described above, when the atmospheric pressure value Pair is lower than the pressure reference value P0, the start-temperature threshold value Teops of the electric oil pump EOP is corrected to be reduced and/or the command duty ratio Rduty for the electric oil pump EOP is corrected to be increased, depending on the first pressure difference ΔP1, so that the coil temperature Tcoil of the stator coil 48 is actively reduced whereby the dielectric strength Vins, which tends to be reduced with reduction of the atmospheric pressure value Pair, is held not smaller than the required dielectric-strength value Vlim. Consequently, it is possible to ensure the required dielectric-strength value Vlim even if the thickness of the film of the stator coil 55 is made thin. On the other hand, when the atmospheric pressure value Pair is higher than the pressure reference value P0, the start-temperature threshold value Teops of the electric oil pump EOP is corrected to be increased and/or the command duty ratio Rduty for the electric oil pump EOP is corrected to be reduced, depending on the second pressure difference ΔP2, thereby making it to possible to reduce the amount of the electric-power consumed by the electric oil pump EOP, by limiting the operation of the electric oil pump EOP, while making the dielectric strength Vins not smaller than the required dielectric-strength value Vlim.

FIG. 5 is a flow chart showing a main part of a control routine executed by the electronic control device 90, namely, a control routine that is executed for ensuring the required dielectric-strength value Vlim even during running of the vehicle in highlands without increasing the overall size of the rotating machine MG. This control routine is executed in a repeated manner during running of the vehicle.

The control routine is initiated with step S10 corresponding to control function of the pump control portion 100, which is implemented to determine whether the pressure difference ΔP (=P−P0) of the atmospheric pressure value Pair relative to the pressure reference value P0 is smaller than zero or not. When an affirmative determination is made at step S10, step S20 corresponding to control function of the pump control portion 100 is implemented to calculate the first electric voltage difference ΔV1, based on the pressure difference ΔP and the change rate α that is obtained from the relationship shown in FIG. 3 , and then to calculate the first temperature difference ΔT1 (by which the coil temperature Toil is to be reduced for enabling the dielectric strength Vins to be the required dielectric-strength value Vlim), based on the first electric voltage difference ΔV1 and the change rate β that is obtained from the relationship shown in FIG. 4 . Step S20 is followed by step S30 corresponding to control function of the pump control portion 100, which is implemented to obtain the correction amount ΔTeops1 of the start-temperature threshold value Teops of the electric oil pump EOP, for reducing the coil temperature Tcoil by the first temperature difference ΔT1, and then to calculate the corrected value of the start-temperature threshold value Teops, by subtracting the correction amount ΔTeops1 from the start-temperature threshold value Teops as the currently set value. Alternatively, step S30 is implemented to obtain the correction amount ΔRduty1 of the command duty ratio Rduty of the electric oil pump EOP for reducing the coil temperature Tcoil by the first temperature difference ΔT1, and then to calculate the corrected value of the command duty ratio Rduty by adding the correction amount ΔRduty1 to the command duty ratio Rduty as the currently set value.

Referring back to step S10, when a negative determination is made at step S10, the control flow goes to step S40 corresponding to control function of the pump control portion 100, which is implemented to calculate the second electric voltage difference ΔV2, based on the pressure difference ΔP and the change rate α that is obtained from the relationship shown in FIG. 3 , and then to calculate the second temperature difference ΔT2 (by which the coil temperature Toil of the stator coil 48 is allowed to be increased), based on the second electric voltage difference ΔV2 and the change rate β that is obtained from the relationship shown in FIG. 4 . Step S40 is followed by step S50 corresponding to control function of the pump control portion 100, which is implemented to obtain the correction amount ΔTeops2 of the start-temperature threshold value Teops of the electric oil pump EOP, for increasing the coil temperature Tcoil by the second temperature difference ΔT2, and then to calculate the corrected value of the start-temperature threshold value Teops, by adding the correction amount ΔTeops2 to the start-temperature threshold value Teops as the currently set value. Alternatively, step S50 is implemented to obtain the correction amount ΔRduty2 of the command duty ratio Rduty of the electric oil pump EOP for increasing the coil temperature Tcoil by the second temperature difference ΔT2, and then to calculate the corrected value of the command duty ratio Rduty by subtracting the correction amount ΔRduty2 from the command duty ratio Rduty as the currently set value.

At step S60 corresponding to control function of the pump control portion 100, the command signal Seop is outputted for starting the operation of the electric oil pump EOP when the coil temperature Tcoil becomes the corrected value of the start-temperature threshold value Teops, or for operating the electric oil pump EOP with the drive current that is controlled in accordance with the corrected value of the command duty ratio Rduty.

As described above, in the present embodiment, the operation of the electric oil pump EOP is controlled depending on the pressure difference ΔP between the pressure reference value P0 and the atmospheric pressure value Pair, so that the operation of the electric oil pump EOP is appropriately controlled. Therefore, even when the atmospheric pressure value Pair is changed, the electric oil pump EOP is operated depending on the change of the atmospheric pressure value Pair whereby the coil temperature Tcoil of the stator coil (48, 55) is adjusted depending on the atmospheric pressure value Pair so that the dielectric strength Vins of the stator coil (48, 55) is sufficiently ensured. Consequently, it is possible to sufficiently ensure the dielectric strength Vins of the stator coil (48, 55) while suppressing increase of the overall size of the rotating machine (MG1, MG2).

In the present embodiment, at least one of the start-temperature threshold value Teops and the command duty ratio Rduty of the electric oil pump EOP is changed depending on the pressure difference ΔP, so that the electric oil pump EOP can be controlled depending on the pressure difference ΔP. Further, when the atmospheric pressure value Pair is lower than the pressure reference value P0, the first temperature difference ΔT1 that is the amount of change (reduction) from the temperature reference value T0 of the coil temperature Tcoil of the stator coil (48, 55), for causing the dielectric strength Vins of the stator coil (48, 55) to become the required dielectric-strength value Vlim, is calculated, based on the pressure difference ΔP, so that the required dielectric-strength value Vlim can be ensured by controlling the electric oil pump EOP such that the coil temperature Tcoil is reduced by the first temperature difference ΔT1. Therefore, where the thickness of the film of the stator coil (48, 55) is made thin, the required dielectric-strength value Vlim can be ensured while increase of the overall size of the rotating machine (MG1, MG2) is suppressed. Further, when the atmospheric pressure value Pair is higher than the pressure reference value P0, the second temperature difference ΔT2 that is the amount of change (increase) from the temperature reference value T0 of the coil temperature Tcoil of the stator coil (48, 55), for causing the dielectric strength Vins of the stator coil (48, 55) to become the required dielectric-strength value Vlim, is calculated, based on the pressure difference ΔP, so that an electric-power consumption amount can be reduced with reduction of output of the electric oil pump EOP, by controlling the electric oil pump EOP such that the coil temperature Tcoil is increased by the second temperature difference ΔT2.

In the present embodiment, when the atmospheric pressure value Pair is lower than the pressure reference value P0, the start-temperature threshold value Teops is reduced by the correction amount ΔTeops1 that is increased as the first temperature difference ΔT1 is increased. As the first temperature difference ΔT1 is increased, the start timing of the operation of the electric oil pump EOP is advanced more whereby the coil temperature Tcoil can be reduced by the first temperature difference ΔT1. When the atmospheric pressure value Pair is higher than the pressure reference value P0, the start-temperature threshold value Teops is increased by the correction amount ΔTeops2 that is increased as the second temperature difference ΔT2 is increased. As the second temperature difference ΔT2 is increased, the start timing of the operation of the electric oil pump EOP is delayed more whereby the amount of the electric power consumed by the electric oil pump EOP can be reduced by an amount corresponding to reduction of the operation time of the electric oil pump EOP.

In the present embodiment, when the atmospheric pressure value Pair is lower than the pressure reference value P0, the command duty ratio Rduty of the electric oil pump EOP is increased by the correction amount ΔRduty1 that is increased as the first temperature difference ΔT1 is increased. As the first temperature difference ΔT1 is increased, the flow rate of the oil outputted from the electric oil pump EOP is increased whereby the coil temperature Tcoil can be reduced by the first temperature difference ΔT1. When the atmospheric pressure value Pair is higher than the pressure reference value P0, the command duty ratio Rduty of the electric oil pump EOP is reduced by the correction amount ΔRduty2 that is increased as the second temperature difference ΔT2 is increased. As the second temperature difference ΔT2 is increased, the flow rate of the oil outputted from the electric oil pump EOP is reduced whereby the amount of the electric power consumed by the electric oil pump EOP can be reduced in proportion with increase of the second temperature difference ΔT2.

While the preferred embodiment of this invention has been described in detail by reference to the drawings, it is to be understood that the invention may be otherwise embodied.

For example, in the above-described embodiment, the calculations of the electric voltage difference ΔV and the temperature difference ΔT are made at one of steps S20, S40, which is dependent on whether the pressure difference ΔP(Pair−P0) is a negative value or not. However, the calculations of the electric voltage difference ΔV and the temperature difference ΔT may be made at a same step, irrespective of whether the pressure difference ΔP (Pair−P0) is a negative value or not. Described specifically, it is possible to formulate a relational expression for calculating the electric voltage difference ΔV from the relationship represented by the broken line in FIG. 3 , and then to calculate the electric voltage difference ΔV by applying the pressure difference ΔP into the formulated relational expression. Similarly, it is possible to formulate a relational expression for calculating the temperature difference ΔT from the relationship represented by the solid line in FIG. 4 , and then to calculate the temperature difference ΔT by applying the electric voltage difference ΔVin to the formulated relational expression.

In the above-described embodiment, the electric voltage difference ΔV is calculated from the pressure difference ΔP, and then the temperature difference ΔT is calculated from the electric voltage difference ΔV. However, it is possible to formulate a relational map or a relational expression for obtaining the temperature difference ΔT from the pressure difference ΔP, and then to directly calculate the temperature difference ΔT by applying the pressure difference ΔP into the formulated relational map or expression.

In the above-described embodiment, one of the start-temperature threshold value Teops and the command duty ratio Rduty of the electric oil pump EOP is corrected depending on the pressure difference ΔP. However, both of the start-temperature threshold value Teops and the command duty ratio Rduty of the electric oil pump EOP may be corrected. That is, it is possible to correct (change) at least one of the start-temperature threshold value Teops and the command duty ratio Rduty of the electric oil pump EOP, as needed depending on the pressure difference ΔP.

In the above-described embodiment, the relational map, which is used for obtaining the correction amount ΔTeops1 of the start-temperature threshold value Teops in the case in which the atmospheric pressure value Pair is lower than the pressure reference value P0, and the relational map, which is used for obtaining the correction amount ΔTeops2 of the start-temperature threshold value Teops in the case in which the atmospheric pressure value Pair is higher than the pressure reference value P0, are prepared independently of each other. However, these relational maps may be replaced by a single relational map that is used for obtaining the correction amount of the start-temperature threshold value Teops in both of the case in which the atmospheric pressure value Pair is lower than the pressure reference value P0 and the case in which the atmospheric pressure value Pair is higher than the pressure reference value P0.

In the above-described embodiment, the relational map, which is used for obtaining the correction amount ΔRduty1 of the command duty ratio Rduty in the case in which the atmospheric pressure value Pair is lower than the pressure reference value P0, and the relational map, which is used for obtaining the correction amount ΔRduty2 of the command duty ratio Rduty in the case in which the atmospheric pressure value Pair is higher than the pressure reference value P0, are prepared independently of each other. However, these relational maps may be replaced by a single relational map that is used for obtaining the correction amount of the command duty ratio Rduty in both of the case in which the atmospheric pressure value Pair is lower than the pressure reference value P0 and the case in which the atmospheric pressure value Pair is higher than the pressure reference value P0.

In the above-described embodiment, the oil outputted from the electric oil pump EOP is supplied into the cooling pipe 74. However, the oil outputted from the mechanical oil pump MOP as well as the oil outputted from the electric oil pump EOP may be supplied into the cooling pipe 74. The present invention is applicable also to this modified arrangement. In this modified arrangement, the operation of the electric oil pump EOP is controlled depending on the pressure difference ΔP and also depending on, for example, a flow rate of the oil supplied from the mechanical oil pump MOP during operation of the engine 12.

In the above-described embodiment, the driving apparatus 10 is to be used for the hybrid electric vehicle including the engine 12, the first rotating machine MG1 and the second rotating machine MG2. However, the present invention is applicable to a driving apparatus that is to be used for a hybrid electric vehicle including an engine and a single rotating machine, and a driving apparatus that is to be used for an electric vehicle including at least one rotating machine each serving as a drive power source without including an engine serving as a drive power source.

It is to be understood that the embodiment described above is given for illustrative purpose only, and that the present invention may be embodied with various modifications and improvements which may occur to those skilled in the art.

NOMENCLATURE OF ELEMENTS

-   -   48: stator coil (coil)     -   55: stator coil (coil)     -   70: cooling device     -   84: cooling oil passage     -   90: electronic control device (control device)     -   94: atmospheric pressure sensor     -   MG1 first rotating machine (rotating machine)     -   MG2: second rotating machine (rotating machine)     -   EOP: electric oil pump     -   ΔP: pressure difference     -   P0: pressure reference value     -   T0: predetermined temperature reference value     -   ΔT1: first temperature difference     -   ΔT2: second temperature difference     -   Vins: dielectric strength     -   Vlim: required dielectric-strength value     -   Teops: start-temperature threshold value     -   ΔTeops1, ΔTeops2: correction amount     -   (correction amount of start-temperature threshold value         correction amount)     -   Rduty: command duty ratio     -   ΔRduty1, ΔRduty2: correction amount (correction amount of         command duty ratio) 

What is claimed is:
 1. A cooling device for a rotating machine that is to be provided in a vehicle, the cooling device comprising: an electric oil pump; a control device configured to control operation of the electric oil pump; and a cooling oil passage for applying oil outputted by the electric oil pump, to a coil of the rotating machine, wherein the control device is configured to control the operation of the electric oil pump, depending on a pressure difference between a predetermined pressure reference value and an atmospheric pressure value that is detected by an atmospheric pressure sensor.
 2. The cooling device according to claim 1, wherein the electric oil pump is to be operated with a drive current supplied to the electric oil pump, and starts to be operated when a temperature of the coil of the rotating machine becomes not lower than a start-temperature threshold value, and wherein the control device is configured to change at least one of the start-temperature threshold value and a command duty ratio that is a command value of a duty ratio of the drive current supplied to the electric oil pump, depending on the pressure difference.
 3. The cooling device according to claim 1, wherein, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to calculate, based on the pressure difference, a first temperature difference that is an amount of change from a predetermined temperature reference value of a temperature of the coil of the rotating machine, for causing a dielectric strength of the coil to become a required dielectric-strength value, and wherein, when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to calculate, based on the pressure difference, a second temperature difference that is an amount of change from the predetermined temperature reference value of the temperature of the coil of the rotating machine, for causing the dielectric strength of the coil to become the required dielectric-strength value.
 4. The cooling device according to claim 3, wherein, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to reduce the start-temperature threshold value, and wherein, when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to increase the start-temperature threshold value.
 5. The cooling device according to claim 3, wherein, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to increase the command duty ratio, and wherein, when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to reduce the command duty ratio.
 6. The cooling device according to claim 4, wherein, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to reduce the start-temperature threshold value, by a correction amount that is increased as the first temperature difference is increased, and wherein, when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to increase the start-temperature threshold value, by a correction amount that is increased as the second temperature difference is increased.
 7. The cooling device according to claim 5, wherein, when the atmospheric pressure value is lower than the predetermined pressure reference value, the control device is configured to increase the command duty ratio, by a correction amount that is increased as the first temperature difference is increased, and wherein, when the atmospheric pressure value is higher than the predetermined pressure reference value, the control device is configured to reduce the command duty ratio, by a correction amount that is increased as the second temperature difference is increased. 